AeroVironment, Pasadena (1971-1989)

AeroVironment (AV) is an American compagny headquarted in Monrovia, California. It was founded in 1971 by three Caltech scientists: Paul MacCready, Peter Lissaman and Ivar Tombach. Today, AV’s core business are Unmanned Aicraft Systems (drones) and military gear. It wasn’t always the case, and up to the mid 1990’s AV did play a significant role in the fields of Wind Energy and Atmospheric Boundary Layer Science. As Mr. MacCready recalls in 2003:

We had a peculiar goal for the company: It was to do work in the type of things that appealed to us. But a lot of things appealed to us, so you couldn’t set out a direction for the company. We just felt there were enough projects of the type that we would find interesting, and slowly projects arose.

Tom Zambrano, thanks to whom some AV material has already been published on Aeolians.net, has kindly allowed me to post the below video; it illustrates some of these projects which were AV’s core business in the 1970s and 1980s. I will focus on three of them in this blog post: Aircraft wakes, Air quality studies, and Wind Energy.

If like me you are an AV fan, you will find many delightful materials in Caltech Archives’ Paul B. MacCready papers:

• Aerovironment Inc. “The Anemometer” Vol. 5, No.5 (1981-07) |link|.
• Aerovironment Inc. “A Plan for Development” (1971-07-26) |link|.
• Caltech Archives. “AV Leaflets and Publications” (1973-2001) |link|.
• Caltech Archives. “AV Strategic Business and Organizational Plans (276 items)” (1973-2001) |link|.
• Caltech Archives. “AV Overview of Activities (72 items)” (1986) |link|.

Aircraft wakes (1970-1979)

Aircrafts leave trails of vortices behind them, and these vortices are a threat to the other airplanes. After a first airplane has taken off, it is necessary for the next aircraft in line to wait for these vortices to dissipate; this is something you surely recall. How large are these vortices, and how to they form? How long does it take for them to dissipate? These are some of the questions which AV (and many others) addressed by making experiments in the 1970s.

See below some of AV’s contributions to this question:

• MacCready P.B., Bate E.R. “Aircraft Vortex-Wake Effects on Particle Transport, Breakup and Coalescence” (1973-01) |link|.
• Lissaman P., Crow S.C., MacCready P.B., Tombach I.H., Bate E.R. “Aircraft Vortex Wake Descent and Decay under Real Atmospheric Effects” (1973-10) |link|.
• Tombach I.H., Bate E.R., MacCready P.B. “Investigation of the Motion and Decay of the Vortex Wake of a Light Twin-Engine Aircraft” (1974-10) |link|.
• Tombach I., Lissaman P.B.S, Mullen J.B., Barker S.J. “Aircraft Vortex Wake Decay Near the Ground” (1977-05) |link|.

Here is an extract from the last publication in the list:

A multi-faceted experimental and analytical research program was carried out to explore the details of aircraft wake vortex breakdown under conditions representative of those which would prevail at low altitudes in the vicinity of airports.

Three separate approaches were taken simultaneously. Flight tests with Lockheed L-18 Lodestar and Boeing 747 aircraft flying over ground-based instrumentation provided data on overall vortex behavior, on the vortex ages at the time of onset of instabilities, and on the changes in the vortex velocity fields which resulted from vortex breakdowns. Analytical work on stability theories identified conditions under which vortices could undergo unstable decay. Experimental tests in a water tank looked at the internal instability of vortices, and also shed light on vortex motion near the ground. Finally, a heuristic modeling approach resulted in a simple representation of the relationship between the times of vortex breakdowns and the ambient turbulence levels.

Although a detailed mechanism for vortex breakdowns was not found, a universal function, usable for all aircraft, was developed for predicting vortex breakdown times within a factor of two error. It was also shown that vortex break downs do not generally result in total dissipation of the vortex energy, but rather a residual organized motion of significant intensity often persists after bursting of a smokemarked vortex has been noted to occur.

Of interest, is the influence of the atmospheric stability on the behaviour of the vortices (a similar behaviour to that of wind turbine wakes):

Air quality studies

Another of AV’s area of expertise was air quality, the division was headed by Ivar Tombach. Much of the work was performed in California and in the Mid-West.

Projects ranged from Motorways to cement factories and oil & gaz projects; see an overview below.

The Products division produced a #plethora of sensors and instrumentation systems, in particular RaDARs and SoDARs, which were utilised for air quality studies. As you surely recall, the vertical structure of the atmosphere is very important for pollution studies, as pollutents can get trapped near the ground during, for example, situations where a layer or relatively warmer sits on top a layer of cold(er) air.

See below some engineering and scientific publications (some of them deal with the projets alluded to in Tom’s slideshow):

• MacCready P. B., Baboolal Lal B., Lissaman P.B.S. Diffusion and turbulence aloft over complex terrain (1974) |link|.
• AVACTA — Air Pollution Model for Complex Terrain Applications (1978)
• Zannetti P. An Improved Puff Algorithm for Plume Dispersion Simulation (1981) |link|.
• Lyons, C.; Tombach, I. Willamette Valley field and slash burning impact air surveillance network data evaluation, v. 2. Pasadena, CA: Aerovironment Inc (1979) |link|.
• Tombach I.A. and Mathai C.V. A Critical Assessment of Atmospheric Visibility and Aerosol Measurements in the Eastern United State (1987) |link|.
• National Park Service. Air Quality in the National Parcs |link|.

Wind Energy studies

AV’s Aeroscience division and staff was involved in many pionneer Wind Energy projects, and I have had the chance to write about some of these already on this blog. These projects can be grouped in three categories:

1. Wind turbine design and aerodynamics: see for instance:
   • (Wilson R.E and Lissaman P.B.S) Applied Aerodynamics of Wind Power Machines (1974) |link|
   • (Wilson R.E, Lissaman P.B.S and Walker S.N.) Aerodynamic Performance of Wind Turbines (1976) |link|
   • (Lissaman P.B.S) Energy effectiveness of arrays of wind energy collection systems |link| and associated reports.
2. Wind Resource Assessments (regional studies and wind atlases), see examples below:
   • (Zambrano T.G, Walker Stel N., Baker R.W) Wind Energy Assessment of the Palm Springs-Whitewater Region. Prepared for Southern California Edison Compagny, and the California Energy Commission (1980-02) |link|.
   • (Lissaman P.B.S, Zambrano T.G., Walker S.N.) Wind Energy Assessment of the Palm Springs-Whitewater Region. Third International Symposium on Wind Energy Systems (1980-08) |link|.
   • (Zambrano T.G., Arcemont G.J.): Wind Energy Assessment Studies for Southern California Vol 2 of 4. Prepared for Southern California Edison Compagny, and the California Energy Commission (1981-05) |link|.
   • (Zambrano T.G., Arcemont G.J.): Wind Energy Assessment Studies for Southern California Vol 3 of 4. Prepared for Southern California Edison Compagny, and the California Energy Commission (1981-05) |link|.
   • (Zambrano T.G., Arcemont G.J.): Wind Energy Assessment Studies for Southern California Vol 4 of 4. Prepared for Southern California Edison Compagny, and the California Energy Commission (1981-05) |link|.
   • (Zambrano T.G.) Assessing the Local Windfield with Instrumentation. Prepared for Pacific Northwest Laboratory (1980-10) |link|.
3. Lastly: micrositing, wind & site studies for specific, commercial wind farm projects. I put in this category the work carried out on AVENU (the commercial name of AVFARM) and the (so far, vastly confidential) commercial advisory services. See the text below for more details.

I would like to focus on AVENU, which was a micrositing software developed and sold by AeroVironment. It was called AVFARM in its infancy, but the commercial name was AVENU; see the final report below:

• (Lissaman P.B.S, Foster D.R.) Final report. Operational model for the design of optimal wind farm arrays. Work performed under contract NO.DE-AC03-86ER80422 for the US DOE (1989-09) |link|.

There are several interim reports as well:

• (Lissaman, Foster, Hibbs 1987): Operational Model for the Design of Optimum Wind Farm Arrays (1987-01) |link|.
• (Lissaman P.B.S, Foster D.R.) Operational model for the design of optimal wind farm arrays. Technical progress report for the period 15 November 1987 through 14 February 1989. Work performed under contract NO.DE-AC03-86ER80422 for the US DOE (1989-03-25) |link|.
• (Lissaman P.B.S, Foster D.R.) Operational model for the design of optimal wind farm arrays. Technical progress report for the period 15 February 1988 through 14 May 1988. Work performed under contract NO.DE-AC03-86ER80422 for the US DOE (1988-06-30) |link|.
• (Lissaman P.B.S, Foster D.R.) Operational model for the design of optimal wind farm arrays. Technical progress report for the period 15 May 1988 through 14 August 1988. Work performed under contract NO.DE-AC03-86ER80422 for the US DOE (1988-11-01) |link|.
• (Lissaman P.B.S, Foster D.R.) Operational model for the design of optimal wind farm arrays. Technical progress report for the period 15 August 1988 through 14 November 1988. Work performed under contract NO.DE-AC03-86ER80422 for the US DOE (1988-12-15) |link|.

A couple of studies have used AVENU, see the following papers:

• (Botta G., Castagna R., Borghetti M., Mantegna D.) Wind analysis on complex terrain — The case of acqua spruzza. Journal of Wind Engineering and Industrial Aerodynamics (1992) |link|.
• (Kambezidis H.D., Asimakopoulos D.N., Helmis C.G.) Wake measurements behind a horizontal-axis 50 kW wind turbine. Solar & Wind Technology (1990) |link|.

So what were AVENU’s core capabilities ? Maybe does it make sense to compare them with that of WAsP at the time (see Section 4.1.2 of the final report for all the details):

• Flow model: like WAsP, AVENUE relies on a “Jackson and Hunt” type of flow model (neutral) to account for the topography. The model is called MS3DJH-3R, and can handle roughness changes (through a varying surface shear stress perturbation). The final report provides some examples of validation in complex terrain, see below.

• Wake model: the wake model is the AV-Lissaman model, and it includes the effect of complex terrain, see illustration below.

• Implementation and useability: AVENU is, from a user-interface perspective, alike today’s WindPRO – that is: with a nice graphical user interface and modules that are fitted to the needs of the industry (see screenshots below). It runs on an Apple OS while WAsP runs on MS-DOS; and provides park layout optimisation and uncertainty/revenue/bankability modules while WAsP is principally aiming at single turbines or small parks. A “turbulence” module is briefly mentioned as part of the development plan. Yet, AVENU seems a bit slow: two to four hours for converting orography and roughness maps to computational grids, and about one hour per wind direction for the wind flow module. In all, the documentation states that setting up a project could take up to 24 hours. Of course, as opposed to WAsP, the flow features are here calculated across all the domain, and not just at the turbine location, so it is hard to compared the performance of the two codes. I would bet they are similar, when compared on an equal basis. AVENU differs from WAsP in the sense that it does not compute a regional wind climate at the geostropic level, thereby it cannot be used to produce wind atlas like WAsP. AVENU is more alike today’s desktop CFD models, to that regard.

AVENU has not met commercial success, as we know today WAsP became the preffered tool for performing micrositing calculations. It is difficult to find trace of AVENU and its users. The documentation provided above has kindly been released from its copyright by the Office of Scientific and Technical Information (OSTI) upon my request – may they be thanked ! Some basic research leads to AVENU and WaSP being mentioned together in a early 1990’s EU project (“Wind measurements and modelling in complex terrain“) – see also the above mentioned paper on the complex terrain sites in Italy (same project); but really there isn’t much. If, dear reader, you know something about AVENU, please get in touch ^^.

Conclusion

We have browsed through twenty years of fun projects and legendary characters at AeroVironment, from it foundation in 1971 to the release of AVENU, a micrositing tool conccurent to WAsP, in 1988. If you are not already a fan of AV, you should quickly become one, just by reading the wonderful, clear reports by Lissaman, Zambrano, Tombach and friends. May they be thanked and long remembered, for all their efforts and the great work they accomplished !